python global variable

There are two primary types of variables in Python: global variables and local variables.
A global variable is accessible throughout the code, whereas a local variable is limited to its defined scope.

In the diagram above, the global variable (x) is available throughout the code, while the local variable (z) is confined to block 3.

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Local Variables

Local variables are confined to their defined scope.
In the following example, x and y are local variables:

def sum(x,y):
    sum = x + y
    return sum

print(sum(8,6))

Here, x and y are only accessible within the sum function and are not recognized outside it.
Thus, attempting to print a local variable outside its scope, like this:

print(x)

will result in an error.

Global Variables

In contrast, a global variable is available throughout your entire code.
Below is an example of a global variable, z:

z = 10

def afunction():
    global z
    print(z)

afunction()
print(z)

Whether inside or outside a function, the global variable z is accessible.
Moreover, you can modify a global variable within a function, impacting its value throughout the entire program:

z = 10

def afunction():
    global z
    z = 9

afunction()
print(z)

After invoking afunction(), the value of the global variable changes for the entire program.

Exercise

Both local and global variables can coexist in a single Python program.
Examine the following code and predict its output:

z = 10

def func1():
    global z
    z = 3

def func2(x,y):
    global z
    return x+y+z

func1()
total = func2(4,5)
print(total)

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